Study On Properties Of Epoxy Resin Modified By Hyperbranched Polymers With Hydroxy Terminal Groups

In this paper,hyperbranched poly(urea-urethane)s(HPU) was synthesized by "one-pot" method,and the influence of HPU on epoxy resin(EP) was studied. Hyperbranched poly(amide ester)/epoxy resin(HBP/EP) composite was prepared with HBP as an additive.The mechanical properties and thermal stability of composites were studied by using of impact testing,stretching testing,bending testing,DSC and TGA.FTIR and SEM were used to investigate the curing and toughing mechanism.Comparing the two kinds of hyperbranched polymers,the structure influence of hyperbranched polymers on the epoxy resin were analyzed.(1) Isophorone diisocyanate(IPDI) and diethanol amine(DEA) were used to synthesize hyperbranched poly(urea-urethane)s in an one-pot method in the surrounding of Dimethylacetamide(DMAc).The structure of HPU was determined by FTIR and NMR.The performances of HBP were studied by DSC,X-ray and TGA.PEG was grafted on HPU to end capping and modify HPU.According to the modifying,the Tg of HPU became lower and the performance of dissolving became better.(2) Methyltetrahydrophthalic anhydride(MeTHPA) and imidazole were used as curing agent and accelerant respectively.The hyperbranched poly(urea-urethane)s was added to epoxy resin and the properties of HPU/EP system were studied.The content of curing agent and accelerant,the curing time and temperature were optimized.The results showed that the mechanical properties and the thermal degradation temperature decreased.The hyperbranched poly(urea-urethane)s ended capping by PEG made the mechanical properties of EP better than that of HPU. Comparing to pure EP,the mechanical properties of composite still decreased.The optical microscope showed that hyperbranched poly(urea-urethane)s was incompatible with epoxy resin.Because of the difference of structures between hyperbranched poly(urea-urethane)s and epoxy resin,HPU could not be used to modify the toughness of EP.(3) Hyperbranched poly(amide ester) with a lot of hydroxy terminal groups was used to prepare the HBP/EP composite by powder mixing.The system was homogeneous,and it showed that the two kinds of polymers had good compatibility. The results indicated that water resistance of EP was improved by the addition of HBP. Mechanical properties were excellent when the content of HBP was 10%.Impact strength was improved from 12.27 kJ/m~2 to 29.78 kJ/m~2.The tensile strength and flexural strength also increased in a certain extent.It showed stress whitening phenomenon obviously while it was bended or impacted.The corresponding glass transition temperature decreased slightly,and the storage modulus conspicuously increased in glass state.The corresponding thermal degradation temperature varied slightly according to DSC and TGA.In order to compare with powder mixing,the composite was prepared by solution mixing.The result showed that impact strength was improved within the low content of HBP.However,with the increasing addition of HBP,the content of acetone that was used for dissolving HBP increased,too.Then the impact strength of HBP/EP composite decreased,tensile strength and flexural strength became instable.(4) The reinforcing and toughening mechanism about HBP was discussed by the use of FTIR and SEM.The result showed that HBP had reacted with curing agent,accelerated the curing behavior and enhanced the crosslinking density.Impact fracture morphology of toughened EP behaved cell-like and tearing feature,and the stripes of stress tended to disperse.The structure of cavity and benzene in HBP and crosslinking density made the epoxy resin have the optimal mechanical properties with suitable content of HBP.